#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <map>
#include <cmath>
using namespace std;
int main1004()
{
	double sum = 0;
	for (int i = 0;i<12;i++)
	{
		double money;
		cin >> money;
		sum += money;

	}
	double avg = sum / 13;
	cout.setf(ios::fixed);
	cout.precision(4);
	cout << "$" << sum / 12 << endl;
	return 0;
}